2009

SPA

CE

OD

YSS

EYa guide to DEEP SPACE

THE PILLARS OF CREATIONIn the constellation of Serpens lies the Eagle Nebula, (right) a giantcloud of interstellar gas and dust. Here new stars are being born,condensing out of the nebula. The radiation from these stellar infantsis energizing the gas, causing it to glow. A closer look at the Eagle Nebulareveals intriguing structures including the famous Pillars of Creation.These dark structures are columns of cool gas, mainly hydrogen and dust,that serve as incubators for new stars. Astronomers have detected blobsof much denser gas inside the Pillars, these appear to be forming solarsystems. Eventually the new star will become visible as their radiationblows away the surrounding material. Each Pillar is several light yearslong. The Pillars and the surrounding nebula are 7000 light years fromEarth, so we see them as they were 7000 years ago. Possibly they nolonger exist, the shockwave from a nearby exploding star may alreadyhave ripped through them and we will see this happeninga few thousand years from now - or maybe tomorrow.

THE HUBBLE SPACE TELESCOPEProbably the most famous astronomical satellite ever,the Hubble Space Telescope has given us amazing viewsof the wonders of the cosmos. Placed into orbit by aSpace Shuttle mission in 1990, the HST initially sufferedfrom a focussing problem. This meant that its imageswere blurred. A NASA investigation revealed that itsmain mirror had been manufactured incorrectly and thetesting that should have disclosed this error had beencancelled as a money-saving measure.Happily astronauts were able to install a new componentto correct this problem in 1993. Since then the HST hasprovided unparalleled views of deep space objects.Many of these are stunningly beautiful and have becomefamiliar through their reproduction on posters, albumcovers and in science fiction movies. Visits by Space Shuttle crewsto service the HST and replace worn-out components have extended its life but theend is in sight. The next servicing mission will be the final one, and all being wellthe HST will be replaced by the bigger still James Webb Space Telescope in 2013.

TO THE ENDS OF THE UNIVERSE Since the invention of the telescope 400 years ago, astronomers have been striving to seefurther and further into the heavens. Every time you look up at the night sky, you are lookingback in time. The light we can see left the stars and galaxies hundreds or even thousands ofyears ago. In fact, some of the stars we can see may not even be there any more.We live in a galaxy called the Milky Way, a vast flat spiral of hundreds of billions of stars.Our Sun and its family of planets, including the Earth, circle the Milky Way’s centre in along slow orbit. The Milky Way’s size defies human comprehension: a beam of lightwould take 100 thousand years to travel from one side to the other.

Until the 1920s many astronomers believed that our galaxywas essentially the entire Universe. Other galaxies werevisible but were thought to be ‘spiral nebulae’, relativelysmall objects inside the Milky Way. Then Edwin Hubble,a flamboyant character of an astronomer, recognized a typeof star called a Cepheid in the Andromeda Nebula, the largestof these spiral nebulae. Cepheids, stars which pulse at a rategoverned by their brightness, are extremely useful ‘standardcandles’ for astronomers, who can easily tell how far away aCepheid is just by observing how long it takes to cyclefrom minimum to maximum brightness. Hubble did thecalculations and discovered that the Andromeda Nebulawas very distant indeed (2.2 million light years away is theaccepted figure today), so far in fact that it could only be a galaxy in its own right.The Universe must be far larger than previously thought. At the time this was verycontroversial, but Hubble was about to create an even greater stir. However tounderstand what he did, we firstly will need to discuss light.

HOW FAR ARE THE STARS?Light travels as a wave, and hence it has a wavelength. If youimagine waves in the ocean, their wavelength is the distancebetween each crest. Just for a moment think about thefamiliar colours of the rainbow (or spectrum). At one side westart with red which has a long wavelength, next orange withslightly shorter wavelength, moving through the colours toblue and violet the wavelengths get smaller and smaller.Light waves from moving sources are stretched orcompressed by the motion. If an object is coming towards youits light is blueshifted meaning the light waves are squeezedtogether appearing more bluish, similarly if it is receding thelight is redshifted. This is called the Doppler Effect and is very useful in many aspects of astronomy.For example, by studying the light from a star we can tell if it is coming in our direction (blueshift)or moving away (redshift), or we can use the Doppler Effect to measure its speed. Between 1912 and1917, astronomer Vesto Slipher was using the Doppler Effect to measure the speed of ‘nebulae’, atthe time still believed to be nearby objects inside our own galaxy. To his surprise, of twenty fivenebulae, four were blueshifted (and therefore coming towards us) and the rest were redshiftedand hence moving away from us. By the late 1920s Hubble was using the 100 inch Mount Wilsontelescope, the largest in the world at the time, to look at distant galaxies. By 1929 he had catalogued46 galaxies by their distance and speed (measured by the Doppler Effect). The conclusions wereunmistakeable and confirmed Slipher’s results. Firstly most galaxies are receding from our galaxy,Secondly, the degree of redshift (and therefore the galaxy’s velocity) is directly proportional to itsdistance away. In other words, if a galaxy was twice as far away as another, it would appear to betravelling twice as fast. This is now called Hubble’s Law, and it made his name. Hubble’s Law openedup a new way of determining intergalactic distances. If we measure the redshift of a galaxy,we will know its velocity, and by Hubble’s Law, we will automatically know its distance away.

EDE71610 deep space:deep space poster AW 13/1/09 14:21 Page 1

2009 SPACE ODYSSEY

Don't miss tomorrow's Star Chart poster

www.belfasttelegraph.co.uk

Today’s free poster

DEEP SPACE

2009 SPACE ODYSSEY

Don't miss tomorrow's Star Chart poster

www.belfasttelegraph.co.uk

Today’s free poster

DEEP SPACE

THE BIG BANG THEORYEdwin Hubble’s observations showed that the Universe isexpanding. This implies that in the past the Universe wasmuch smaller than it is now. Then the galaxies would havebeen closer together, going further back in time therewould have been a time when they were squeezed closertogether still and ultimately there would have been a timewhen everything was at a single point. In the 1930s, Belgianphysicist and priest Georges Lemaître suggested that if theevident expansion of the universe was reversed until itcould contract no further, all the mass of the Universe would be squeezed into what hecalled the ‘primeval atom’ or ‘cosmic egg’. This had exploded, expanding outwards tocreate the Universe we see today. In 1948 two physicists Ralph Alpher and GeorgeGamow calculated that most of the chemical elements could have been created in thismassive explosion. Their work implied that heat from this explosion should be spreadthroughout space, appearing as a faint radio (or microwave) emission. Alpher andGamow did not believe it would possible to detect this background radiation.

SPACE AND TIMEAstronomers accept that, rather than being twoseparate entities, space and time are one, sometimescalled spacetime. Rather than simply saying wheresomething is located, it would be more correct to say howlong it is there for too. This is based mainly on the workof Albert Einstein, specifically his theory of GeneralRelativity. Einstein’s theories had other importantimplications, one of which is that an object’s gravitydistorts spacetime. Rather than saying a planet exerts agravitational pull towards it, it is truer to say its gravitybends the space around it. The path of a beam of light passing a star would be curvedas it passes through the warped space around the star. This has been observed andastronomers are now well aware of the phenomena of ‘gravitational lensing’ when theimage of a distant galaxy is distorted by the gravity of other galaxies between it andthe Earth. Stranger still as space and time are one, gravity distorts time too. Time runsslower near a massive object such as a star than it in empty space. This is not just someobscure prediction about the distant Universe, experiments with very accurate atomicclocks have verified that time moves faster on the Earth’s surface than it does on highmountain peaks. This difference is so tiny as to be imperceptible to human sensesbut would be obvious near a black hole. If an astronaut could leave her spacecraftto somehow safely approach a black hole, her crewmates would see her appearto slow down until she became almost frozen in place.

Albert Einstein

Edwin Hubble

Content & Images supplied courtesy of:

Poster design by Jonathan Simms

THE SEARCH FOR E.T.Searching for life elsewhere in the Universe is a fascinat-ing endeavor. Astronomers in the 1800s used telescopesto search for signs of life and even civilization elsewherein the Solar System. Some even believed they saw signsof intelligent life on Mars in the form of a grid of canalsacross the Red Planet’s surface. Illustrations and maps ofMars published by NASA as late as the early 1960s stillshowed these. Disappointingly, visits to Mars byspaceprobes from the mid-60s onwards revealed it to be more barren and inhospitablethan previously thought. There is still a possibility that life arose on Mars billions ofyears ago when conditions on the planet were milder, and perhaps some bacteria-likeorganisms cling on to life under the surface. We probably will not know if this is trueor not until people travel to Mars to explore. Elsewhere in the Solar System, there isevidence for oceans of water under the icy surfaces of Jupiter’s moon Europa andSaturn’s moons Enceladus and Titan. These may be the best prospects for life-bearingsites in the Solar System. Could bizarre aquatic life swim in the inky depths of thesealien seas? Given the difficulties of sending a mission to drill through the crusts ofthese distant moons, we will probably not know the answer for centuries.

Since 1995 astronomers have discovered 300 or so planets orbiting other stars.The vast majority so far discovered are huge gas giant planets like Jupiter or Saturn butas technology improves we ought to find worlds more like Earth. To find life out thereall we can do at present is try to listen for radio signals from alien beings. This is theSearch for Extra-terrestrial Intelligence (SETI) and is conducted mainly as a spare-timeproject by some astronomers. At present no government funds SETI research, butprivate groups such as the Planetary Society have paid to scan the sky for artificialsignals. Grandest of these efforts is the Allen Telescope Array, 42 linked 6 metre radiotelescopes funded by Microsoft billionaire Paul Allen. We humans have sent our ownmessages into space. Plaques and discs of data were been bolted to the Voyager andPioneer deepspace probes should any space travelling ETs find them.

Many astronomers would say that alien life is a possibility, but one astronomer, FrankDrake, has tried to work out the number of extraterrestrial civilizations active in thegalaxy. The Drake Equation uses estimates of how common planets are around otherstars, how many are suitable for life, on how many actually develop life and so on togive ‘N’ the number of alien civilizations. Unfortunately, most of these values are littlemore than guesses at the moment, so values of N vary from hundreds of thousandsto just one (ourselves!). Perhaps the Cosmos is full of life or perhaps we are alone.Either possibility is awe-inspiring.

British scientist Fred Hoyle championed a rival explanation called the Steady Statetheory and fiercely disagreed with this explosion theory which he sarcastically called‘the Big Bang Theory’. This name stuck and has been used ever since.The Steady State theory is no longer accepted. In the early 1960s, two engineers ArnoPenzias and Robert Wilson, were employed by the Bell corporation to find a sourceof radio interference picked up in a satellite communications antenna.The interference was a faint but steady radio noise coming from every direction theantenna was pointed. It appeared to come from all over the sky. Penzias and Wilsonconsulted other scientists and realised that they had accidentally discovered theCosmic Microwave Background predicted by Gamow and Alpher.

DARK MATTER96% of the Universe is invisible to us! Astronomers reached this unsettling conclusionby studying galaxies. Observations showed that the spin rates of galaxies are fasterthan they should be, in fact high enough to pull them to pieces, so some unseen forcemust be holding the galaxies together. This could not be the gravity of the stars we seein the galaxies as there are not enough of them. The only reasonable conclusion is thatsome mysterious form of undetectable matter dominates each galaxy. This has beencalled Dark Matter ( because it does not give out any light). Some of it may be tinyblack holes or brown dwarf stars drifting between the stars but most of it seems tobe composed of sub-nuclear particles which have yet to be studied in the laboratory.The unexpected discovery of dark matter shows that there is still so much forus to learn about the Universe.

RADIO ASTRONOMYIn 1930 Karl Jansky was investigating radio interference which was disturbingtransmissions on a trans-Atlantic radio link. Using a giant radio antenna whichcould be pointed in any direction he discovered that some of this radionoise came from the sky and particular the constellationof Sagittarius. Jansky concluded that the radio noiseoriginated in the centre of the Milky Way. This was thestart of radio astronomy, radio astronomy has enabled usto observe a new depth to the Universe. Astronomers usethe natural radio emissions of clouds of hydrogen to mapthe galaxy including regions obscured to our sight.We have been able to explore and chart the core of theMilky Way in great detail and determine that a vast blackhole must dominate its centre. Pulsars, fast-spinningremains of exploded stars were discovered through radioobservations by Portadown-born Jocelyn Bell Burnell.Radio astronomy shows that there is more to theUniverse than meets the eye!

Jodrell Bank radio telescope

EDE71610 deep space:deep space poster AW 13/1/09 14:22 Page 2